In the oil and gas production industries a well known stimulation operation is the use of aqueous acid solutions to enlarge pore spaces and increase permeability of rock matrix in hydrocarbon-producing formations which generally are subterranean formations of oil and gas wells . Such acidizing operations increase the hydrocarbon recovery from the wells. The enlarged pore spaces and increased rock matrix permeability permit an increased amount of hydrocarbon material to reach the well bore and be recovered therefrom. In other words, aqueous acid solutions, for instance hydrochloric acid, are used to dissolve carbonate rock within the wells to increase the flow of hydrocarbons to the well bore.
In such acidizing treatments it is often desirable to increase the viscosity of (viscosify) the aqueous acid solution. Acidic fluids of high viscosity are desired for a number of purposes, including to retard the spend time of the acid so as to increase the time during which the acid fluid remains active, to reduce the loss of acid fluid to the formation, to more efficiently carry any proppant being used to the site of the fracture(s), and to control fracture height and width.
It is generally known in the oil and gas production industries that the viscosity of aqueous acid solutions may be increased by the addition thereto of various gelling agents such as water soluble gums and cellulose derivatives. These agents, however, have limited stability in acid fluids . Synthetic polymeric gelling agents, which also have been used for viscosifying aqueous acid solutions, tend to degrade from high shear encountered in pumps, tubing and performations in the wellbore during the injection of the acidizing fluid. High molecular weight gelling agents are also often difficult to disperse in aqueous acid solutions, require a great amount of agitation for full viscosity development, and may be ineffective at the high temperatures encountered during well stimulation operations.
Well stimulation acidizing methods include the pressurized injection (typically by pumping down) of acidizing fluid into the well bore and hydrocarbon-producing formation and hydraulic fracturing methods wherein by the use of higher pressures the formation is fractured by the hydraulic pressure of the acid solution. In the latter method proppants are often used, such as sand or other like material, to prop the fracture open, holding apart the walls thereof. In some instances the acidizing fluid may be introduced into the well after a fracturing procedure to remove acid soluble material from the well.
Certain surfactants are known for increasing the viscosity of aqueous acid solutions used for well stimulation operations. In U.S. Pat. No. 4,591,447 there is disclosed a buffered gelling/foaming agent comprising a N,N-bis(2-hydroxyethyl)fatty amine acetic acid salt, an alkali metal acetate salt, acetic acid, and water. In U.S. Pat. No. 4,324,669 certain water soluble organic solvents, that is certain alkanols, ketones, polyhydroxy compounds, ethers, acids, esters, and lactones, in combination with mixtures of ethoxylated fatty amines are disclosed as foaming/gelling agents for aqueous acids.
In well stimulation operations by acidizing methods it is generally desirable to protect metal components of the equipment used from the corrosive effects of the acid(s) being used. Typical acid corrosion inhibitors for metals are generally in the art believed to provide corrosion inhibition by forming a protective film on metal surfaces.
It is an object of the present invention to provide a viscosifier for well stimulation acidic fluid and a viscosified acidic fluid for use in treatinq hydrocarbon-producing formations, which viscosifier is stable in acid fluids, does not degrade from the high shear conditions encountered during the injection of the acidizing fluid, is easy to disperse in aqueous acid solutions, requires little agitation for full viscosity development, and is effective at temperatures up to about 150.degree. F. It is also an object of the present invention to provide a material effective as both an acid viscosifier and corrosion inhibitor, and a viscosified acidic fluid containing same. These and other objects of the present invention are disclosed in more detail below.